Patent document 1: Japanese Patent Laid-Open No. 5-87934
The scintillator crystals are used in many fields as detectors of various radiations, such as X-ray and γ-ray. Required characteristics for the scintillator crystals are somewhat changed depending on their uses, but generally involve:                a high density;        a large fluorescence output by applying radiation;        a high fluorescence attenuation rate:        good radiation tolerance:        a crystal having no deliquescence or cleavability, and easy to be processed        
In these days, taking into account these requirements, crystals adopting active Ce with high
attenuation rate (20-60 ns) are often used. For example, Gd2SiO5:Ce (GSO), Lu2SiO5:Ce (LSO) and the like are used in the medical diagnostic equipments, such as PET (positron emission tomography), but the above-mentioned required characteristics are not necessarily satisfied sufficiently and there are problems that: in GSO, the crystal raising requires high techniques due to strong crystal anisotropy and becomes the hindrance of cost reduction, and in LSO, the fluorescence output has variations between samples.
Also, as the scintillators using Pr, Ce and F, those consisting of Gd2O2:Pr, Ce and F have been known as described in Patent document 1.
However, even among the scintillators according to Patent-documents 1, scintillators with stable characteristics (especially fluorescence output) have not yet been obtained.